Evaporator



M ch 16, 1937.

H. A. WHITESEL EVAPORATOR Filed Dec. 1, 1952 Inventor: Hat-r A. Whitesel,

His Attofhey.

Patented Mar. 16, 1937 UNITED STATES nvaronaron Harry A. Whitesel, Fort Wayne, Ind., asaignor to General Electric Company, a corporation of New York Application December 1. 1932, Serial No. 645.255

9 Claims.

My invention relates to evaporators or cooling units for refrigerating machines.

In household refrigerators the cabinet is maintained below 50 F. and above 32 F. and a range of operating temperatures within these limits is selected according to the requirements of the particular refrigerator. Refrigerating machines are ordinarily equipped with a single evaporator for cooling the cabinet, and this evaporator is also provided with a compartment in which are placed freezing trays. It is desirable that the temperature of the evaporator within the compartment be low enough to freeze quickly the substances placed therein and it is therefore necessary to maintain the evaporator at a temperature considerably below the freezing point. As the air is chilled in passing over the surface of the evaporator it moves downwardly and the warmer air moves in an upward current which produces a continuous circulation of air in the cabinet. This air current absorbs moisture from food in the cabinet, and as the current rises moisture is carried up to the evaporator. is lower than the dew point of the rising air and as a result moisture is condensed on the evaporator. This moisture freezes and in a short period of time the evaporator is covered with frost which continues to accumulate as the cabinet is operated. Frequent defrosting is required in order to keep the evaporator in its best operat-' ing condition. In addition to this, there is another objection in that the air circulating in the a cabinet is maintained at such low humidity that 35 the food is dried.

It is an object of my invention to provide a cooling unit which willeliminate the necessity of frequent defrosting.

Another object of my invention is to provide 40 a cooling unit which will maintain a substantially uniform cabinet temperature under varying operating conditions.

A further object of my invention is to provide a cooling unit which will not cause undue dry- 45 ing of the food in the refrigerator cabinet.

A still further object of my invention is to provide a simple and compact cooling unit having separate portions operating at different temperatures and having automatic means for maintain- 50 ing a predetermined temperature difference between the separate portions of the evaporator.

Further objects and advantages of my invention will become apparent as the following description proceeds and the novelty which char- 55 acterizes my invention will be pointed out with Here the temperature particularity in the claims annexed to and forming a part of this specification.

For a better understanding of my invention, reference may be had to the accompanying drawing, Fig. 1 of which is a perspective view, partly 5 in section, of a cooling unit embodying my invention; Fig. 2 is a detailed sectional view of the evaporator headers connected through a constant pressure differential valve; and Fig. 3 is a side elevation of a refrigerator cabinet having a re- 10 frigerating machine employing my improved cooling unit.

Referring to the drawing, in Fig. 1, I have shown a cooling unit embodying my invention and comprising an outer hollow evaporator l0 1 forming a freezing compartment containing an inner freezing evaporator II in the form of a shelf. These evaporators are of the flooded type and are operated at different pressures in order to maintain the desired temperature difierence 2 between the two evaporators. Evaporator I0 is formed of inner and outer shells i2 and I3, respectively. The outer shell i3 is formed with corrugations i4 communicating at the top with a transverse corrugation forming a manifold i5, and is closely fitted about the shell i2. Contacting parts of the shells are connected by some suitable means such as brazing or line welding. The outer shell I3 is provided with a plurality of flanged fins l6 secured to the corrugations i4 to increase the effective heat absorbing surface of the evaporator. A cylindrical header i1 is provided on the shell i3 opening into the space formed by the corrugations i4 and i5. The rear end of this hollow evaporator is closed by a plate i8, shown in Fig. 2, and the front end may be provided with a door a part of which is shown at I9 to prevent circulation of air from the refrigerator cabinet through the ice freezing compartment. The inner or low pressure evaporator II is supported from the upper inside wall of the outer evaporator and is formed by upper and lower sheets 20 and 2i, respectively, the lower sheet 2i being provided with corrugations. 22 and a transverse corrugation forming a manifold 23 closed at their ends by downwardly bent'edges 20' of the upper sheet 20. These sheets are connected around their edges and along the contacting corrugations in a manner similar to that used in connecting the shells i2 and i3 of the hollow evaporator Ill. The upper sheet 20 of the inner evaporator is provided with a cylindrical header 24 communicating with the corrugations 22 and 23 and which is secured in an opening 25 in the shell i2 of the evaporator III as shown at 23 and extends partially into the header II. The construction of the cylindrical headers I1 and 24 can be seen by referring to Fig. 2 of the drawing. Flanged base 21 of the header I! is formed in the wall l3 of the evaporator l3, and the top 28 of the header I1 is joined to the side Wall as shown at 23. The header 24 is joined to an upturned flange 30 on the sheet 20 as shown at 3|. These Joints may be made by welding, brazing, or in any other suitable manner. Liquefied refrigerant is supplied to the header I! through a conduit 32. In order to maintain a difference in pressure between the evaporators l and II, I provide a differential pressure valve 33 which admits liquid and gaseous refrigerant to the header 24. During the refrigerating cycle the evaporator I0 is preferably operated over a range of pressure such that during a portion of the cycle it is at a temperature above 32 F.; this 20 provides defrosting of the evaporator surface during each cycle, and suiilciently minimizes drying of the air in the cabinet. It will be apparent,

however, that under certain required conditions temperature with this evaporator will be much less affected by variations in room temperature or by opening of the cabinet door. The evaporator II is maintained at a lower pressure than the evaporator I0 such that the temperature of the evaporator II will be low enough to freeze substances placed therein within a short time. The refrigerant which is vaporized in the evaporator ll passes through the suction conduit 34 back to the compressor of the refrigerating machine.

Evaporators l0 and II are spaced apart to accommodate freezing trays 35 supported on the evaporator H and freezing trays 33 supported in close relation to the under side of evaporator II by ribs 31 formed in the bottom portion of the shell I2 of the evaporator l0. Although the evaporator I and the ice trays 35 and 36 are maintained at a temperature considerably below the freezing point of water, there will be practically no formation of frost around these parts of the cooling unit because there is no substantial circulation of air over the surface of the evaporator I, particularly when the door I9 is provided.

The constant pressure differential valve 33 shown in Fig. 2, which maintains the desired difference in pressure between the evaporators l0 and II includes a cylindrical casing 38 secured to a body 39 on top of the header 24 and a bellows 40 mounted within the casing and arranged to actuate a hollow valve stem 4| having a flange 42 sealed to the bellows. The valve stem 4| is slidably mounted in a, guide 43 in the body 39 and a valve 44 formed on the stem 4| rests on a seat 45 in the end of a sleeve 46 which is fitted into and sealed to the header 24. Openings 41 are provided in casing 38 and the valve stem 4| is made hollow so that the bellows will be subject to the pressure of evaporator l0 externally and to the pressure of evaporator internally. A compression spring 48 biases the bellows to its expanded position to seat the valve 44. This spring is calibrated so that the desired pressure difference will be maintained between the evaporators.

In the operation of this valve mechanism as long as the pressure within the bellows 43 in addition to the force of the compression spring 48 is suillcient to overcome the external pressure in the header I! the valve 44 will remain closed, but as soon as the pressure in the header ll becomes too great the valve will open and permit the refrigerant to flow from the header into the header24 .to re-establish the desired pressure diflerence and close the valve.

In Fig. 3 I have shown a cooling unit 49 of the construction above described as employed in a household refrigerator cabinet 50. This refrigerator cabinet is provided with a compression type refrigerating system including a motor and compressor arranged within a casing secured -to a removable top of the cabinet. During operation of this compression system refrigerant is compressed within the casing whence it flows through the cooling coil of condenser I52, is liquefied and flows to a float valve chamber 53. When a predetermined amount of liquid refrigerant has collected in the float valve chamher, a float rises and the liquid refrigerant flows down through the conduit 32 into the header H of the cooling unit 49. The liquid refrigerant is vaporized in the evaporators l0 and II and is then withdrawn therefrom by the compressor through suction conduit 34. This cycle is con,- tinuously repeated during the operation of the machine, the motor of which is controlled by an automatic switch mechanism 54 in response to a thermostatic device arranged within the cabinet 50. The thermostatic device is arranged to start the motor at an upper temperature limit and to stop the motor at a lower temperature limit.

When the upper limit is above 32 F. and the lower limit below 32 F., the refrigerating system operates so that the evaporator is defrosted during each cycle. The pressure difference between the evaporators l0 and H is selected so that the evaporator It will maintain the compartment of the cabinet 50 at a proper temperature, and so that the inner evaporator II will be maintained at a sufliciently low temperature for freezing purposes.

Although I have shown a particular embodiment of my invention in connection with a compression refrigerating machine, I do not desire my invention to be limited thereto, and intend in the appended claims to cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. A cooling unit for refrigerators comprising two evaporators one within the other and spaced apart, and means for maintaining a higher pressure within the outer evaporator than within the inner evaporator during normal operation.

2. A cooling unit for refrigerating machines comprising an outer evaporator, a flat evaporator within and spaced from said outer evaporator, a header on each of said evaporators, means including a differential pressure valve and providing communication between said headers for maintaining said outer evaporator at a. higher pressure than said flat evaporator during normal operation. I

3. A cooling unit for refrigerating machines comprising an outer evaporator and an inner evaporator spaced from said outer evaporator,

means for maintaining the temperature of said outer evaporator periodically above and below 32 F., and means including a valve and dependent upon the pressures in said evaporators for maintaining the temperature 0! said inner evaporator sufliciently low for freezing purposes. 4. A cooling unit for refrigerating machines comprising an outer evaporator, a second evaporator arranged within and spaced from said outer evaporator, headers on said evaporators,

a portion of the header on said second evaporator forming a common wall between said evaporators, and means including a differential pressure valve in said common wall for maintaining a higher pressure in said outer evaporator than in said second evaporator during normal operation.

5. A cooling unit for refrigerating machines comprising an outer evaporator, a second evaporator within and spaced from said outer evaporator, means for supplying refrigerant to said outer evaporator, means for removing vaporized refrigerant from said second. evaporator, and means including a difierential pressure valve and providing communication between said headers for maintaining said outer evaporator at a higher pressure than said second evaporator during normal operation.

6. In combination, a refrigerator cabinet and a cooling unit within said cabinet and comprisng two evaporators one within the other and spaced apart, and means for maintaining a higher pressure within the outer evaporator than within the inner evaporator during normal operation.

7. In combination, a refrigerator cabinet and a cooling unit, said cooling unit comprising an outer evaporator, a flat evaporator within and spaced from said outer evaporator, a header on each of said evaporators, and means including a difi'erential pressure valve and providing communication between said headers for maintaining said outer evaporator at a higher pressure than said flat evaporator during normal operation.

' 8. In combination, a refrigerator cabinet and a cooling unit arranged therein, said cooling unit comprising an outer evaporator and an inner evaporator spaced from said outer evaporator, means for maintaining the temperature of said outer evaporator periodically above and below 32 F., and means including a valve and dependent upon the pressures in said evaporators for maintaining the temperature of said inner evaporator sufllciently low for freezing purposes.

9. A cooling unit for {reirigerators comprising an outer flooded evaporator and an inner flooded evaporator spaced from said outer evaporator, and means including a valve providing communication between said evaporators and dependent upon the pressures in said evaporators for maintaining a predetermined difference of temperature between said evaporators during normal operation.

HARRY A. WHITE-BEL. 

